The manual says 0.050-0.060 for 10:5:1 compression and below. That seems really extreme to me. My engine is 10:5:1 and I set my gap at 0.045. Anyone running with the gap they recommend with any issues?

 

If you look at how an "MSD" system operates it's easy to see why the manufacturer would specify a larger than stock gap for the plugs . "MSD" stands for "Multiple Spark Discharge" and means that in the same amount of time an old fashioned points & coil setup could fire one spark at the plug's electrodes (per firing event or "power stroke") the MSD fires several sparks in that same amount of time . This results in more chance of all the fuel in that one compression stroke getting lit . Interestingly the slower the engine is turning the more sparks are allowed , and as the RPM increases the number of sparks per firing event is reduced . The higher RPM's fewer sparks are still of an intensity that would make a points setup blush , the increased lower rpm multiple sparks being more of a function of overcoming the basic CDI's somewhat poor idle/ low rpm firing performance .

The above info was lifted in condensed form directly from MSD's website

 

I read that before also. It seems people think 0.060 is too large regardless. I personally don't want to pull my plugs and re-gap to find out if 0.060 works-lol Runs fine at 0.045. Just curious if anyone is actually running a gap that large.

 

Well the larger gap gonna take more spark energy to jump the gap but the MSD box should make plenty enough energy for that. The larger/hotter spark will reduce miss fires. But the problem with the hotter spark it's gonna eat up the cap, rotor terminals and spark plug electrodes faster. And on a weaker stock ignition the extra energy required to jump the plug gap will take from the total spark energy and reduce the duration of the spark duration. At least that's the science I've read about it. No I don't have a labratory and didn't prove it but I recall the large gaps in stock HEI that Olds used back in the 70's didn't continue for long.

 

The larger the plug gap, the higher the voltage that gets developed across it. The higher the voltage, the more stress there is on EVERYTHING on the HV side of the system: coil, rotor, cap, wires. The more stress, the sooner they'll fail and need to be replaced.

Run no higher of a gap than you can tell any difference from. "Difference" being measured in some combination of, more power, less pinging, easier starting, smoother idle, better gas mileage, etc. etc. etc. I.e. if you set it to .045" like a stock system, and opening it up to .060" doesn't make the engine run better in some way, then it's doing no good in exchange for shorter lifetime of all those other parts. Put it back stock. OTOH if it DOES make a difference, in ways that are worth about DOUBLE the maintenance on all those other parts, then go for it.